The British Tertiary Igneous Province: Potassium--argon Ages of the Antrim Basalts

Twenty-one K-Ar dates on thirteen lavas from Garron Point, Antrim, Northern Ireland yield a minimum age of 49·9±2·2 My. It would appear that this large thickness (>250 m) of lava was extruded over a period of at most a few million years, in agreement with the results of earlier palaeomagnetic work. There is a correlation between the degree of alteration and apparent age of the samples suggesting that the lavas have lost variable amounts of radiogenic argon.